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Numerical Under & Over Voltage Protection Relay Type : MVT 181


MVT 181 is a numerical true RMS single pole relay consists of two elements. Each element can be selected for under voltage function or over voltage function or switched off. The characteristics setting, voltage setting and time multiplier setting are independently settable for each element and the voltage setting is in terms of voltage. Hence this relay can be used as a two stage under voltage or two stage over voltage protection.

Multiple Characteristics:
There are four operating characteristics for over voltage function and two operating characteristics for under voltage function.

Overvoltage Characteristics:

Definite Time Lag (DTL)
Long Time Inverse (LTI)
Extremely Inverse 1(El 1)
Extremely Inverse 2(El 2)

Undervoltage Characteristics:

Definite Time Lag (DTL)
Extremely Inverse 1(El 1)

Two elements:
Two stage O/V Two stage U/V Or one O/V and one U/V

The relay is provided with two status inputs, one of which is to be connected across the circuit breaker auxiliary contact 52a. From this the circuit breaker closed or opened condition is found out. This information is used to introduce a time delay between successive switching of the capacitor banks which allows the capacitor bank to discharge to a safer value after disconnected from a live network. This timer function is a settable one and its output (N/O) contact is used in the closing circuit of the circuit breaker. The completion of this time delay is also indicated by ^TIMER^ LED in the front fascia. In addition the same status input can be used for Trip circuit supervision also.

During other under voltage and over voltage applications this timer function can be disabled or used as an independent timer function.

Trip Circuit Supervision:
Pre-closing and post-closing supervision of the trip circuit and trip supply is possible with this relay. A low value of DC current is passed through the entire trip circuit to monitor the trip coil, its auxiliary switch and the associated wiring. One of the status input is connected across the tripping contact and another status input is connected across the 52a contact (auxiliary contact of the circuit breaker) in series with the trip coil. During trip circuit fail condition the monitoring current flow ceases and the energised status input drops off and the relay gives a contact output to indicate this condition. In addition to this contact an LED is provided in the front fascia to indicate the ^T.C. FAIL^ condition. A time delay of approximately 400 msecs has been given to avoid false trip circuit fail indication at the time of normal tripping. Thus trip circuit supervision is the integral part of the relay. If this function is not required the same can be put off in the setting menu.

Standard Features
Numerical, true RMS measurementDrawout modular case (150X151mm cutout )
Compact designNon-volatile memory for trip indication
Self-monitoring facility7 segment LED display
Status indication LEDsSealable front cover to prevent unauthorised access
2 stage under/over voltage (27/59)Wide voltage setting ranges
Multiple inverse characteristics8 output contacts
Timer for Capacitor bank rechargingTrip circuit supervision

Technical Manual
MVT- 181Manual.pdf

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